1. Field of the Invention
The present invention relates to an electric mirror control device and an electric mirror control method that automatically tilt the mirror surface of a door mirror when a vehicle goes back so that a driver can easily check a road at the rear side of the vehicle.
2. Description of the Related Art
A back mirror device for a door mirror or a fender mirror of an automobile is configured such that only when a switch for controlling a mirror is operated, a direct current motor for controlling a mirror surface is activated to change the angle of the mirror surface in the right-left direction and the up-down direction.
The mirror surface can be tilted in various directions from a center supporting point provided at the back of the mirror surface. More specifically, a pivot axis provided to either the right or left of the center supporting point and another pivot axis provided to either upper part or lower part of the center supporting point are moved forward or backward to change the angle of the mirror surface in the right-left direction and the up-down direction. Accordingly, the mirror surface can be tilted in any direction in combination of the right-left angle change and the up-down angle change.
Each of the pivot axes for the right-left angle and the up-down angle is moved forward or backward by a different direct current motor, and the only motor whose switch is operated is driven to adjust the angle of the mirror surface in the direction controlled by the motor.
In addition to the above mechanism adjusting a mirror surface by a switch operation, some outer door mirrors are further provided with a mechanism that automatically tilts down a mirror surface at a predetermined angle set in advance when the transmission is shifted to the reverse, and tilts up the mirror surface to the position before the mirror surface was tilted down when the transmission is shifted to another position, such as the drive position, from the reverse.
When a driver drives his or her automobile backward into a garage, it is preferable that the driver is allowed to check an area around the rear wheels rather than an area right behind the automobile to eliminate blind spots. Thus, a back mirror device is configured to tilt down the mirror surface when the transmission is in reverse and to return automatically the mirror surface to the position before it was tilted down when the transmission is shifted to any position other than the reverse. This mechanism is configured in such a manner that the motor of two motors which changes the up-down angle is rotated to tilt down the mirror surface in a predetermined amount when the transmission is in the reverse, and is rotated to tilt up the mirror surface in the same amount when transmission is shifted to a position other than reverse.
In conventional electric mirror control devices, a target tilt-down angle to which an outer door mirror is tilted down is set in advance, each of an up-down angle and a right-left angle is detected by a sensor, the mirror surface is tilted down until the output voltage of the sensor reaches the sensor output voltage value corresponding to the target angle when the mirror surface is tilted down, and the mirror surface is tilted up until the output voltage of the sensor returns to the sensor output voltage value before the mirror surface is tilted down. When the outer door mirror is tilted down, a feed forward control is performed on the sensor value (as disclosed in JP Unexamined Patent Publication (Kokai) No. 2003-200783).
In such a outer door mirror described above, when sensors provided by different manufactures are used for the purpose of reducing cost, the control device has to be adjusted in accordance with each of the sensor specifications of the different manufactures.
FIG. 6 is a graph showing the difference of detection output voltages output when the same angular change is detected by sensors with different specifications.
As shown in this graph, the sensor made by the manufacturer A outputs 0.2V for the angle change of 5 degrees, and the sensor made by the manufacturer B outputs 0.5V for the same angle change while the sensor made by the manufacturer D outputs 1.0V for the same angle change.
Thus, there has been a problem that when sensor specifications are different, the control device has to be adjusted in accordance with each sensor specification.
Moreover, the different sensor specifications can be mixed up so that the control device may be adjusted or installed wrongfully if sensor specifications of the manufactures have a similar proportionality constant.